4.2 bell housing for THM400 trans

Just contemplating swapping the BW66 for a THM400, in the thoughts it’d be a less expensive, more serviceable option.

Any words of advice appreciated!

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I think only the DS 420 had the 400 behind the six, so that’s a rare adapter.

BW is an American trans, parts should not be an issue?


I’d go with something more modern, personally.

If you wanna stay with the older stuff, go with the THM350. IMO.

Less parasitic, smaller, still plenty tough


Fair enough!

How available are bells/kits for a 350?

What more modern–not computer controlled–trans would you recommend?

I have a line on a “good” BW66 in California.

Also looking here.


Looks like a MUCH better solution, than rebuilding the BW66.

I have two BW66s you may have, one supposedly rebuilt, but I think you would be far better off with the GM overdrive conversion. John recommends the 700R4, which is what I’m trying to put in a Mk10 (probably the 1st one), but my transmission specialist recommends the 4L60, which is a later version without the hassle of a manual cable. You simply buy an electronic control box for the kick-down.

Those are the options that look the best: given I have to remove the body, to swap out the gearbox, I’d like to do this once.

If the BW66 was local… maybe.